Pass the 'last' parameter of print_signal() through to
print_raw_param(); this fixes a problem where we weren't printing
the comma separator for strace of rt_sigaction() when the signal
was an unnamed (ie realtime) one:
  6856 rt_sigaction(230xf6fff870,0xf6fff8fc) = 0
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>